Butterfly valves are well known and commonly used in the automotive industry. These butterfly valves are usually designed to control the air intake in an air distributor for a fuel injection device using a more or less open butterfly shutter. When the engine idles, this valve has to allow just the right minimum amount of air to pass to ensure that the engines runs. During an acceleration phase, when the driver of a vehicle presses on the accelerator pedal, the butterfly valve has to make it possible to increase the amount of air by instantaneously opening the shutter. In order to ensure flexibility during an acceleration phase, some butterfly valves are designed to allow air to pass through progressively when the butterfly shutter opens. For this purpose, the active inner surface of the valve's housing, i.e. the surface which co-operates with the shutter between its open and closed positions, presents a complex form, provided in particular with a radius of curvature downstream from said shutter in its opening zone.
As a rule, butterfly valves are made of metal and for example of molded aluminum. The housings made in this way generally undergo machining to adjust the internal dimensions according to the shutter. In the case described, for example, in the publication EP-A-109 792 where the housing of the butterfly valve comprises two opposing recesses arranged in the butterfly shutter's opening zones to allow the progressive flow of air when opening. These recesses are achieved by machining, which implies a high cost. Furthermore, for each type of engine, there is a corresponding type of valve with a housing provided with a specific active inner surface according to the variation in the air flow rate required to achieve optimum engine running conditions. It is therefore necessary to provide as many molds for manufacturing housings as types of valves.
It is a well known fact that industrialists are constantly seeking to reduce raw material, manufacturing, assembly and storage costs, as well as reduce the weight of the parts. As a result, some manufacturers have made butterfly valve housings out of molded synthetic material. Two of these embodiments are described in publications FR-A-2 674 573 and FR-A-2 694 963. Nevertheless, the butterfly valves obtained do not make it possible to ensure time-constant air flow rates. Indeed, the material used is generally thermoplastic which is sensitive to variations in humidity and variations in the ambient temperature as well as that of the fluid being conveyed. The result of this is substantial variations in the internal dimensions of the housing, and consequently, the air flow rate for a given position of the shutter. These variations in air flow rate have an effect on the carburation and generate increased pollution from the exhaust gas.
Other butterfly valves are manufactured according to the so-called dual injection process using various materials as described in the publication FR-A-2 687 601 where the body of the valve is molded first, followed by the butterfly shutter. The shutter thus presents absolutely the same form as the body. When operating, there is therefore a risk of the shutter getting stuck in the body caused, in particular, by the shrinkage which is bound to be different due to the fact that the parts do not have the same external shapes and due to variations in humidity and temperature which generate dimensional variations. This manufacturing method does not make it possible to adapt the external shape of the shutter with the internal shape of the body. What is more, the shutter comprises two disks designed to guide it in rotation in said body. This system is totally inefficient throughout time. In the publication EP-A-482 272, the body also serves as a cavity for the shutter. Its form will therefore depend on that of the body without there being any possibility of adapting it. It is not possible to provide a relief on the shutter's external surface to avoid jamming. Furthermore, a Z-shaped shutter generates quite considerable ventilation pressure losses.
Another embodiment of butterfly valve is disclosed in the publication EP-A-0 023 133, this valve being equipped with a ring-shaped insert provided in the conduit and inserted between the housing and shutter. This ring is metallic, presents a basic annular shape and is encompassed by the duplicated molded housing in thermoplastic material. The purpose of this valve is to ensure complete tightness when the shutter closes by means of various seals provided on either side of the ring, between the ring and the housing and between the ring and the butterfly shutter's shaft. An additional metal sleeve is also provided inside the housing on either side of the ring. This embodiment is consequently very complex and costly, taking into account the large number of parts which have to be assembled before duplicate molding the housing and it can only fit one type of engine. Furthermore, complete tightness is generally prohibited in the planned application to avoid the risks of jamming the shutter.
Other embodiments exist with reference to the publication WO-A-96 07041 which describes a butterfly valve comprised of a body made up of two parts, a ring forming a seat and a butterfly shutter. The various parts are manufactured individually and then assembled, which entails a high manufacturing and assembling cost and requires more space. What is more, it is vital that absolute tightness be achieved between the various parts (both parts of the body and the ring) thereby generating an extra cost. In the event of the butterfly housing being arranged at the end of the distributor, it is subjected to considerable accelerations and vibrations and it therefore has to be very rigid to ensure good mechanical behavior. It is difficult to achieve this rigidity if the housing is comprised of several parts. Some of these drawbacks can be found in the valve dealt with in the publication DE-A-196 15 438, the housing of which is comprised of two parts, the ring and the shutter being obtained by means of a dual injection process. The most critical point is the risk of jamming the shutter in the housing, given the fact that the shutter moves through a position perpendicular to said housing's shaft. What is more, the inside ring presents two shoulders which bring about ventilation pressure losses when fully open and thus penalize the filling of the engine's combustion cylinders.
The object of the present invention is to overcome the above-mentioned drawbacks by proposing an extremely simple butterfly valve comprising the minimum number of parts, which can be produced at low cost, whilst being light and able to suit various types of engines, this valve being designed to be stable from a dimensional point of view, insensitive to variations in humidity and temperature, in order to ensure a constant and highly accurate air flow rate throughout time, even in the closed position.